Shock-wave lithotripsy stone fragmentation treatment employs high-energy shock waves to fragment and disintegrate calculi and it can be broadly categorized according to the pattern of energy transfer to the calculi. In this connection lithotripsy can be classified as extracorporeal and intracorporeal. The comprehensive overview of various lithotripsy methods can be found in various sources, e.g. in the Internet site http://www.bsci.com. In accordance with the acceptable definitions shock-wave extracorporeal lithotripsy is a process, which transfers energy needed for stone fragmentation in the form of shock waves from an outside source through body tissue to the calculi. Extracorporeal shock wave lithotripsy (ESWL) has proven effective in achieving stone fragmentation. However, since the energy wave transmission is indirect, and in order to carry out the treatment successfully it is required precise directional focusing of the energy at the stone through intervening body tissue. This might be associated with damaging of the intervening tissues and therefore additional treatments might be required to take care of the damage.
Intracorporeal lithotripsy utilizes a probe advanced with the aim of endoscope and positioned in proximity to the calculus. The energy, required for fragmentation is transferred through the probe to the calculus and the treatment process is visualized during fragmentation. The mode of energy transfer may be different and accordingly the intracorporeal lithotripsy techniques are divided into following groups: ultrasonic, laser, electro-hydraulic and mechanic/ballistic impact.
The last group comprises, for example, detonating an explosive near the stone and causing the shock wave generated by the explosion to act directly upon the stone and crush it into pieces. An example of such technique is disclosed in U.S. Pat. No. 4,605,003, referring to a lithotriptor comprising an inner tube inserted within an outer slender tube and provided with an explosive layer or a gas-generating layer. By the blasting of the explosive layer or the gas-generating layer, the outer slender tube or the inner tube is caused to collide with the stone and crush it.
An example of mechanical impact technique can be found in U.S. Pat. No. 5,448,363 in which is disclosed an endoscopic lithotriptor provided with a hammer element to periodically strike the stone. The hammer element is pneumatically driven by a linear jet of air causing it to swing through an arc about a pivot to impact an anvil.
There are known also many other patents, disclosing lithotriptors, which operation is based on mechanic/ballistic principle, e.g. U.S. Pat. Nos. 5,722,980, 6,261,298.
An example of laser technique is described in U.S. Pat. No. 4,308,905, concerning multi-purpose lithotriptor, equipped with laser light-conducting fibers, through which the energy required for crushing the stone is conducted.
Ultrasonic technique is relatively popular and because of its safety and usefulness is widely accepted. According to this principle ultrasound probe emits high-frequency ultrasonic energy that has a disruption effect upon direct exposure to the stone. Direct contact of the probe tip and stone is essential for effectiveness of ultrasonic lithotripsy. This technique is implemented in many lithotriptors, e.g. as described in U.S. Pat. No. 6,149,656.
The most relevant to the present invention is electro-hydraulic technique, which utilizes electric discharge, ignited between two electrodes disposed within the probe and producing shock wave, expanding towards the calculus through liquid phase, which surrounds the calculus. In the literature electro-hydraulic lithotripsy is defined as the oldest form of “power” lithotripsy. The electro-hydraulic lithotriptor releases high-energy impulse discharges from an electrode at the tip of a flexible probe, which is placed next to the stone. It is considered as highly effective means of bladder stone shattering and has become an accepted practice for this use. Since the generated during electro-hydraulic lithotripsy treatment shock waves are of sufficient force the probe must not be used 5 mm or closer to soft tissues otherwise severe damage will result.
Since the discharge takes place within liquid phase the calculus is destroyed by virtue of combination of energy of the shock wave, caused by the discharge, hydraulic pressure of the surrounding liquid and collision of fragments in the liquid flow. Below are listed some references, referring to intracorporeal lithotripting devices, utilizing the electro-hydraulic principle.
A typical electro-hydraulic lithotriptor is described in CA 2104414. This apparatus is intended for fracturing deposits such as urinary and biliary calculi as well as arteriosclerotic plaque in the body. The lithotriptor comprises a flexible elongated guide member adapted for insertion within the body, means for supplying a working fluid, a hollow tube mounted on the distal end of the probe, means for initiating an electric spark within the hollow tube from an external energy source, capable of generating pulsed shock waves in the working fluid for impinging the stone and a nozzle, which is made of shock and heat resistant material and mounted on the distal end of the guide member. The nozzle is capable of directing the shock waves to a focal point for impinging the stone. The lithotriptor is provided also with optical viewing system.
In U.S. Pat. No. 2,559,227 is disclosed an apparatus for generating shock. The apparatus comprises a truncated ellipsoidal reflector for reflecting the shock waves and a cavity constituting a chamber for reflecting said shock waves. The cavity has the same truncated ellipsoidal shape, while one of the two focal points of the ellipsoid being disposed in the cavity opposite the truncated part. The cavity is filled with a liquid for transmitting the shock waves, for example oil. The apparatus is provided with a shock wave generator device, conventionally comprising two electrodes disposed at least partly inside said cavity. The two electrodes are arranged to generate an electric arc discharge at the focal point located in the cavity opposite the truncated part. The apparatus has also means for selectively and instantaneously delivering an electric voltage to said two electrodes provoking electric arc discharge between said electrodes thus generating shock waves propagating through the liquid contained in the cavity. The electrodes are made of highly conductive material such as copper or brass and are mounted on an insulator with possibility for adjusting the spacing therebetween.
In DE 19609019 is described an impact probe, provided with at least one electrode guided in the tube. The electrode acts on the object when the probe is longitudinally moved in the direction of the object e.g. a stone. Electro-hydraulic pressure wave is produced at the free end of the probe.
It should be stressed that since the probe in conventional electro-hydraulic lithotriptors is not in physical contact with the calculus many efforts are undertaken to focus the maximum of discharge energy immediate on the calculus. An example of such an attempt is electro-hydraulic lithotriptor, known under the trade name THE AUTHOLITH and manufactured by Northgate Technologies. It should be noted, however, in this lithotriptor the energy of shock wave still is transferred via a layer of liquid, remaining between the discharge gap of the probe and the calculi.
The efficiency of electro-hydraulic lithotriptor in terms of its ability to fragment a calculus depends on voltage and duration of electrical pulses, required for achieving breakdown and initiating the spark discharge, since these parameters are interrelated with the amount of energy, which can be produced by the lithotriptor. Commercially available electro-hydraulic lithotriptors, e.g. lithotriptor RIVOLITH 2280 manufactured by Richard Wolf, are provided with pulse generators, capable to generate pulses with pulse rise time of about hundreds nanoseconds and pulse duration of about hundreds of microseconds.
It can be easily appreciated that since the energy is transferred not immediate to the calculus but via a liquid medium, the amount of energy required for fragmentation should be sufficient to overcome the strength of the calculi and to cause its failure after the energy has been delivered through the working liquid (water or urea or physiologic solution). Electric pulses having duration parameters of commercially available lithotriptors allow producing rather high energies of about 2.5–3 joule, which is sufficient for producing stresses capable to fragment various calculi, appearing in the human body.
Unfortunately, release of such high levels of energy by producing shock waves might be harmful to the adjacent tissues and therefore potentially dangerous for the patient.
The further disadvantage of the known in the art electro-hydraulic lithotriptors is associated with their inability to detect and monitor the onset of fragmentation. Since the pulse generator continues to generate pulses after the calculus has been already fragmented, unnecessary energy is produced and its release unnecessary endangers the patient.
Still further drawback of the electro-hydraulic lithotriptors is associated with the necessity to have numerous electric discharges when it is required to destroy especially large and dense calculus. Since the discharge takes place on the surface of the probe insulation, it deteriorates the insulation of the probe tip and may cause its failure even before the treatment session is completed.
Still another problem of almost all intracorporeal lithotriptors that are intended for destroying renal calculi by bringing mechanical energy of impact or shock wave is the fact that the stone is usually “displaced” with each pulse of energy, leaving the previous place and being “thrown” to another one. This renders the operation complicate and may cause mechanical damage to the surrounding tissue. Physical “anchoring” of the treated stone would be desirable here.
An attempt to solve this problem and to extend service life of the probe and at the same time to improve treatment efficiency without rise of harm to the patient is disclosed in DE 3927260. In this patent is described a probe for electrohydraulic lithotripsy, which is provided with a head made of impact-resistant ceramic in the form of a round bass-rod. The rod has two longitudinal channels into which leads are inserted and anchored by a resin material, the ends of the leads being flush with the end face of the rod. Leads pass to a plug via a flexible hose, which extends over the head.
Nevertheless, this particular solution is not designed for immediate physical contact between the probe tip producing a shockwave and the calculus.
There are known lithotriptors, in which such “anchoring” is possible, e.g. a combined holding and lithotripsy instrument, disclosed in DE 19810696. This combined instrument consists of a highly elastic NiTi alloy and has at least three holding arms, which in their unflexed state are curved in a tulip-like manner. The end of each holding arm is toothed and bent towards the instrument axis. When the holding arms are drawn into the instrument tube or working channel they position themselves on the calculus and grasp it when they are drawn in even further. The holding device is configured around the instrument axis in such a way that the angle between directly adjacent holding arms is never equal to or greater than 180 DEG C. This ensures secure holding and grasping and thus prevents the grasped calculus from escaping sideways. The securely held calculus can then be fully fragmented to fragments of a predetermined size using the lithotriptor, i.e. either mechano-ballistically, or by ultrasound, cryogenically or thermally with laser light.
Unfortunately this construction is not suitable for electro-hydraulic mode of operation since the probe tip is not designed to carry electrodes provided with electric insulation and is not therefore capable of producing shock waves, caused by electrical discharge.
On the other hand there is known for some time a method of so-called high-power electro-impulse destruction of materials, which is based on the fact that applying of electrical impulses with the rise time of not more than 500 nanoseconds to two electrodes positioned on a solid mineral material immersed in water is associated with producing discharge, which does not propagate through the surrounding liquid medium, but rather through the bulk of the solid body. This technology was developed in late fifties in Russia and since then it has been successfully implemented in such fields like crushing and disintegration of hard rocks and ores in mining industry, destructing of concrete blocks in building industry, drilling of frozen ground and extremely hard rocks, crushing of various inorganic materials, etc.
A survey of this technology can be found in a monograph “Basics of electro-impulse destroying of materials”, by Semkin et al., Sanct-Petersburg, Nauka, 1993.
According to this technology two or more electrodes are placed immediate on the surface of a solid body (rock) and very short impulses of voltage U(t) are sent through them. Once an electrical breakdown between the electrodes is initiated, it occurs in the bulk of the solid body and is associated with producing of the breakdown discharge channel that extends within the bulk of the body. The body itself serves as a medium to promote propagation of the electrical breakdown rather than the surrounding medium. Extension of the discharge channel through the body is accompanied by mechanical stresses, which stretch the body and destroy it as soon as the tensile strength of the body is exceeded. In fact in the process of electro-impulse destroying the initiation and propagation of the discharge is similar to a micro explosion within the body. It can be readily appreciated that since tensile strength of a rock is at least an order of magnitude less than its compressive strength, the electro-impulse crushing is associated with consumption of much less energy, than conventional electro-hydraulic crushing.
It has been also empirically established, that the probability of propagation of the breakdown channel through the body is higher when a very short voltage impulses are applied to electrodes, positioned on a solid body immersed in a liquid medium, since the voltage required for the breakdown within the bulk of the body is less, than the voltage required for breakdown within the liquid medium outside of the body.
Unfortunately despite the fact that this technology exists for more than 40 years it still has been employed mainly in mining and building industry for destruction of very large objects like rocks or concrete blocks.
An example of this application is disclosed in WO 9710058, in which is described method of comminuting and crushing solids, for example, blocks of reinforced concrete. In accordance with this method the solid is exploded as a result of shock waves being produced therein.
Unfortunately the obvious benefits of this technology associated with more efficient destruction were never considered for employing in such completely new application, like medicine in general and intracorporeal lithotripsy in particular.
In conclusion it should be emphasized that despite the fact that numerous lithotriptors have been devised there is still a need for a new approach that will ensure efficient, reliable, easy and safe fragmentation of calculi during intracorporeal lithotripsy.